Studies in Crataegus (Rosaceae: Maloideae). XX. Interserial hybridization between Crataegus monogyna (series Oxycanthae) and Crataegus punctata (series Punctatae) in southern Ontario

Abstract

Introduced Crataegus monogyna Jacq. and native Crataegus punctata Jacq. are common and distinct species often co-occurring in southern Ontario. Both taxa are diploid obligate outcrossers with overlapping floral phenologies. Putative hybrids between C. monogyna and C. punctata were examined using morphometric analyses, chromatographic comparisons of leaf phenolics, and crossing experiments. These individuals were morphologically and biochemically intermediate in relation to the two parental taxa and were determined to be diploid. In crosses, F1 progeny were formed between C. monogyna and C. punctata, particularly when C. monogyna was the seed parent. The resulting offspring had leaves morphologically intermediate between adult parental and seedling-type material, whereas their chromatographic profiles were comparable to those of the naturally occurring putative hybrids. Based on these data, interserial hybridization between C. monogyna (Oxycanthae) and C. punctata (Punctatae) was confirmed. Postmating barriers are probable and may account for the rare and sporadic occurrence of the hybrids. Seed set in the natural hybrids appeared to be much lower on average than those of the parental species and failed to germinate under controlled conditions.